The present invention is directed generally to a method of fixing an annular piston onto a piston shaft and more particularly to a method of repairing the piston shaft assembly of a railway car end-of-car cushioning unit.
Many railway cars are equipped with an end-of-car cushioning unit on each end. An end-of-car cushioning unit is basically a hydraulic shock absorber interposed between the coupler arm and railway car frame to absorb impact forces and thereby provide a safe or smoother ride for the railway car.
Each end-of-car cushioning unit includes a piston shaft assembly which is subject to wear and breakage. In fact, the piston shafts are generally provided with an annular recess adjacent one end so that the shaft will intentionally break at the recess under abnormal loads to prevent damage to other more expensive portions of the units. The piston shaft assembly may be replaced with a new piston shaft assembly at considerable expense.
There has not heretofore been developed a method for securely yet inexpensively fixing an annular piston onto a piston shaft. One existing method is by a friction weld or inertia weld, which is accomplished by spinning the piston and shaft in opposite directions such that the friction melts the metal and permanently fuses the piston onto the shaft. Very expensive equipment is required for the friction welding operation, however.
Another possibility is to externally weld a piston onto the shaft but this method has the disadvantages of limited penetration of the weld and the necessity that the welded assembly be heat normalized since the metal gets brittle above 2000.degree. F. For example, the piston shaft assemblies could be placed in a furnace at about 1400.degree. F. for about three hours. A large furnace would be required for the assemblies and some type of crane or hoist would be needed for handling the heavy assemblies.
Neither process provides for use of the original piston from the broken piston shaft assembly.
A primary object of the invention is therefore to provide a method for securely yet economically fixing an annular piston onto a piston shaft.
Another object is to provide such a method which can be readily accomplished with conventional machine shop equipment.
Another object is to provide such a method which does not require a separate heat normalizing process for the piston shaft assembly.
Another object is to provide a method of repairing a piston shaft assembly of an end-of-car cushioning unit wherein the original piston may be salvaged and reused.
These and other objects of the invention are resolved by the method of the present invention, as explained hereinbelow.